This invention relates generally to a removable track for an annular resilient tire, and in particular to a removable track provided with dirt-sealing strips. The track has a substantially inextensible annular belt for mounting on the outer circumferential surface of the tire and wear-resistant metal traction shoes clamped on the radially outer surface of the belt. The track-tire assembly is especially suited for off-the-road use over rock or other sharp or abrasive materials which have caused excessive cutting damage and tread wear of conventional off-the-road tires.
Inflation of the tire produces a tight seal between the belt and the tire; however, wear of the belt under the shoes has been a problem because of dust, dirt, rock particles and other foreign materials entering the space between the shoes and the belt. The accumulation of such foreign material places additional stress on the traction shoe retainers, decreasing fatigue life of the same.
During operation of the track-tire assembly, the traction shoes and belt undergo complex movement. Upon entry and exit of the adjacent traction shoes into the footprint or ground-engaging area of the tire, a torque about a horizontal axis is present in the traction shoe just leaving or just engaging the ground. This torque is caused both by the vertical load imposed upon the traction shoe by the vehicle and tire weight and the torque transmitted from the vehicle axle through the tire and the traction shoe to propel the vehicle. This torque within the traction shoe results in a displacement of its leading edge and trailing edge surfaces that is much more severe than simple articulation which occurs in all metallic vehicle track members or in articulated conveyor belt systems. If the vehicle is turning, an additional different torque will be imposed upon those traction shoes entering, exiting, or fully within the footprint region. This torque is about a vertical axis and causes the axially inner and axially outer portions of the leading and trailing edges of adjacent traction shoes to be at different distances from one another. The movement of adjacent track members in or near to the footprint region may be even further amplified if one of the track members or a portion thereof engages a rock or other non-uniformity on the ground. Such non-uniformity can result in very severe local loading of the track member and annular belt resulting not only in a change of the angle between the leading edge surface and the trailing edge surface but also in a radial shifting of adjacent track members.
Various devices have been proposed for sealing the space between adjacent traction shoes. In U.S. Pat. No. 3,899,220, issued to Grawey, sealing is effected by including transverse raised solid ribs on the belt surface between traction shoes. The leading and trailing edges of adjacent track shoes abut against the raised ridges on opposite sides thereof to effect sealing. Alternatively, sealing grooves may be provided in the belt surface which mate with ridges on the shoes. In U.S. Pat. No. 4,043,609, issued to Vidakovic et al, a transverse rib or plug is positioned between the shoes of adjacent assemblies. Alternatively, the rib or plug is integrally formed of the outer surface of the belt. In both embodiments, the rib portion is formed of a resilient elastomer into a solid body whose sides sealingly engage the leading and trailing edges of adjacent traction shoes. In U.S. Pat. No. 4,046,428, issued to Bauer, sealing is effected by providing a separately manufactured elongated resilient sealing strip having slender ribs or fingers between each pair of adjacent articulated traction shoes.
Such attempts at sealing the spaces between adjacent traction shoes have not proven fully effective. Solid rib or plug designs depend upon compression of the sides of the elastomer rib or plug against the adjacent traction shoe surfaces for sealing. The amount of movement of the traction shoes relative to the seals often exceeds the amount which the rib or plug is compressed thus resulting in loss of sealing engagement. The elastomer cannot be compressed beyond a certain amount without permanent damage or deformation. Thus, the effectiveness of these seal designs is limited by the elastomer's compressive properties. Additionally, movement of one traction shoe is transmitted through the solid rib or ply to affect the adjacent traction shoe. Movement of one traction shoe may result in loss of sealing effectiveness not only to itself but also to its neighbor. If the sealing ribs are not located properly relative to the traction shoe sites, they may not be in sealing engagement with the traction shoes. Solid sealing rib designs require extreme accuracy. Such accuracy is difficult and costly to achieve. Separately maufactured seals may be torn loose under the normally severe operating conditions of the track-tire assembly. Seal designs having multiple slender flexible fingers for engagement with a particular traction shoe are not only difficult to manufacture integral with the belt but are also vulnerable to tearing or other damage. When the seal is adhered to one or both of a pair of adjacent traction shoes, the movement of one traction shoe necessarily effects engagement of the seal with the other traction shoe.
Fillers have been used on articulated conveyor belts to provide an uninterrupted surface. Examples of such arrangements are given in U.S. Pat. No. 3,202,266 to Schmermund. However, the lengths of these conveyor belts are not subject to the stresses and adverse operating conditions under which the traction shoes of a track-tire assembly must operate. Adjacent links of these conveyor belts do not undergo the hereinbefore-described complex movement relative to each other as do adjacent traction shoes. Also, it is not desirable to fill the space between the traction shoe sites at the radially outermost surface because this reduces the traction provided by the shoes and detracts from cleaning of the tread.
With the foregoing in mind, it is a principal object of this invention to provide a fully sealed track belt that prohibits the ingress of soil, rock, and other foreign material between the track shoes during articulation of the belt and shoes and to thereby improve service life.
Another object is to seal each traction shoe so that movement of one traction shoe does not adversely affect sealing of the adjacent shoes.
Another object is to provide for flexing of the sealing ribs upon articulation or radial displacement of the track members to maintain the seal.
A further object is to provide an annular track belt having an integrally molded seal whose sealing effectiveness is less dependent on manufacturing accuracy than known sealed track belts of similar application.
Another object is to provide an annular belt having an integrally molded seal which can be readily removed from the mold after vulcanization.
A still further object is to provide an annular belt having an integrally molded seal having increased resistance to abrasion, cutting, and tearing.
A still further object is to provide an annular belt having an integrally molded seal whose sealing faces are positively urged into contact with the traction shoes through mechanical means.